Cradle of a gear-cutting machine

ABSTRACT

A cradle for a bevelled gear generating machine comprising two slidably mounted tool holding arms pivotably connected to respective levers, each in turn being supported on an axle spaced from the pivot axis of the arms to the levers. Each arm can be pivotably moved about its respective pivotal connection with the lever and each lever can be pivotably moved about its axle, the latter movement being in a direction substantially perpendicular to the pivotal movement of the arm relative to the levers, so that the combined movements of the levers and its respective arm can move the tool carried by the arm along a predetermined closed path. Each tool holding arm is slidably mounted inside a turnable segment within the cradle for setting the tool carried by the arm at a desirable tooth angle of the gear to be machined.

United States Patent 1 Kedrinsky et al.

[ 1 Nov. 6, 1973 CRADLE OF A GEAR-CUTTING MACHINE [76] Inventors: VasilyNikolaevich Kedrinsky,

Profsojuznaya ulitsa, 40, kv. 85, Moscow; Boris Grigorievich Zudov,Zhiluchastok Zavoda Zuboreznykh, Stankov, 31, kv. 24, Saratov, both ofU.S.S.R.

[22] Filed: July 12, 1971 [21] Appl. No.: 161,898

Related U.S. Application Data [63] Continuation of Ser. No. 836,852,July 12, 1971,

1,335,864 4/1920 Stevenson 90/8 Primary Examiner-Gil WeidenfeldAttorney-Waters, Roditi, Schwartz & Nissen [5 7] ABSTRACT A cradle for abevelled gear generating machine comprising two slidably mounted toolholding arms pivotably connected to respective levens, each in turnbeing supported on an axle spaced from the pivot axis of the arms to thelevers. Each arm can be pivotably moved about its respective pivotalconnection with the lever and each lever can be pivotably moved aboutits axle, the latter movement being in a direction substantiallyperpendicular to the pivotal movement of the arm relative to the levers,so that the combined movements of the levers and its respective arm canmove the tool carried by the arm along a predetermined closed path.

' Each tool holding arm is slidably mounted inside a turnable segmentwithin the cradle for setting the tool carried by the arm at a desirabletooth angle of the gear to be machined.

6 Claims, 4 Drawing Figures 1 j \l Z0 a PATENTEU NOV 6 I975 SHEET 1 UF 2PATENTEU xnv 6 ma 3.769.877 SHEET 2UP 2 CRADLE OF A GEAR-CUTTING MACHINEThe present invention relates to gear-cutting machines and, moreparticularly, to cradles for gearcutting machines designed for machiningteeth of straight bevel gears by cutting.

The present invention may be also used for cutting teeth of straightbevel and spur gears, or other similar workpieces, such as toothedcouplings, with matching toothed surfaces.

Known in the prior art is a cradle of a gear-cutting machine whichcomprises a drum having segments mounted therein and carrying slidesused for fixing the tool or cutters. The slides are imparted a rockingmotion by a crank gear and the cradle is provided with a device used toadjust the slides to the length of the generatrix of the pitch cone of agear being machined.

Employment of cutting tools operating in one and the same tooth cavityof a gear being cut for cutting straight bevel gears by a generatingtechnique provides better conditions for cutting by theme] andcompletely identical conditions for machining all the cavities of a gearbeing cut, which contributes to precise manufacture of the latter.However, the aforesaid cradle possesses various disadvantages.

The vertical slides are secured to the front end of the segments throughan intermediate plate and are disposed far outside the generating cradlehousing and, therefore, extend far from the cradle support, whichdecreases the rigidity of the unit and the precision of the machining ofteeth.

The drive of the cutter, mounted on the slide, has a spindle whose axisis inclined to the plane of rotation of the cradle, due to which thetool heads are also inclined, and, to prevent the latter frominterfering with the work head, the workpiece must be placed on a longarbor, which considerably decreases the rigidity of the workpiecefastening and the precision of cutting of a gear.

In the course of its operation, the cutter describes curves that arecharacterized by great convexity, due to which the bottom of the toothspace thus formed is too concave, which is not desirable for manydesigns of toothed gears.

The curve, described by the cutters, is designed for a tooth havingmaximum depth, and cannot be altered during the machine set-up.Therefore, the large radius of the curve at the points of transitionfrom the forward stroke to the reverse stroke remains constant, andduring a great part of their running the cutters perform no cutting,which decreases the machine efficiency.

As a result of this, it is vertually impossible to cut gears, in whichthe hubs protrude forward i.e. beyond the cone center, for in this casethe distance which the cutters extend beyond the faces of the workpieceis strictly limited.

Each time the cradle performs its reverse stroke, the table carrying theworkpiece is retracted together with the workpiece from the tools, whichentails displacement of massive parts which do not come back to theirinitial positions with absolute accuracy, and, therefore, brings abouterrors in the'pitch of the gears being cut.

The present invention contemplates the development of a design of thecradle of a. gear-cutting machine, used for machining teeth of straightbevel gears by tools operating in one and the same tooth-space, that isfree of the afore-mentioned disadvantages and will allow an increase inthe precision of machining of gears.

The afore-said task is accomplished by the provision of a cradle of agear-cutting machine, usedfor machining teeth of straight bevel gears bymeans of tools operating the same tooth space, which cradle comprises agenerating drum having turnable segments mounted therein carrying toolholding arms: or slides. The slides are subjected to a rocking motion,and, a means is employed for adjusting the position of the slides-to thecone distance of the gear beingmachined. In accordance with the presentinvention, each of the slides is pivotally connected to a lever which inturn can be pivoted with respect to the cradle segment, for imparting alongitudinal motion to the slide.

It is expedient that the guides in the segment for the slides beinclined with respect to the axis of symmetry of the cradle at an angleclose to the pressure angle of the gear being cut.

To adjust the arms carrying the tools to the cone distance of the gearbeing machined, the levers are supported by carriages mounted in guidesin the interior of the cradle.

To extract the tool from the tooth space of a gear being machined duringthe idle period before the return stroke it is expedient to use agripper for operating on the levers. The gripper is connected to the rodof a hydraulic cylinder disposed in the cradle drum.

It is also necessary to extract the tool from the toothspace of a gearbeing machined at the end of the forward stroke and to introduce it intothe space upon completion of the reverse stroke, and this is effected bya cam interacting with the lever. v

The following detailed description of a specific exemplary embodiment ofthe present invention is given with reference to the accompanyingdrawings, in which:

FIG. 1 is a longitudinal sectional view of the cradle of a gear-cuttingmachine for machining teeth of straight bevel gears, according to theinvention;

FIG. 2 is a section taken on the line II-II of FIG. 1 showing the leversand a drive for displacing them, according to the invention; a

FIG. 3 is a front elevational view of the cradle; and

F IG 4 is a rear elevational view of the cradle.

A cradle of a gear-cutting machine used for machining teeth of straightbevel gears comprises a generating drum 1 (FIG. 1) having two turnablesegments 2 mounted therein, each of the segments 2 carrying a slide ortool holding arm 4 driven by a crank gear assembly mounted on arespective segment. The crank gear assembly comprises a drive shaft 13,crank-plate 24 with a crankpin 31 mounted thereon and a connecting rod25 of adjustable length whose free end is pivotably connected to thetool holding arm 4. The cradle also comprises a gripper 3 (FIG. 2) usedfor extracting both tools from the tooth space of a gear being machinedat the time of cradle return rotation and means reciprocation in guides11 of the segment 2 and driven by a butt cam 12, positioned on shaft 13of the crank gear.

One end of the pusher carries a roller 14, which con-tacts the face ofthe cam 12, whereas the other (flat) end of the pusher 10 contacts thefree end of the lever 8. The afore-described system is tensioned bymeans of a spring 16. When the cutting gears have great size, the systemmay be tensioned, for instance, by a hydraulic means.

By presetting the required shape of the cam 12, it is possible to obtaina trajectory of cutter movement with minimum transitions between theforward and reverse strokes, which makes it possible to cut gears withhubs ex-tending forward.

The arm 4 carrying the tool is disposed in guides 17 (FIG. 1) in thesegment 2, which guides are inclined at an angle close to the pressureangle of the gear being machined.

The guides 17 are disposed inside the segment 2 of the cradle generatingdrum 1, and it is only the tool holder 5 with the cutter 6 that protrudebeyond the end 18 of the segment 2 facing the cutting zone. The lever 8and its axle 9 are disposed at end 19 of the segment 2 facing theinterior of the cradle (i.e., opposite to the cutting zone).

Due to the afore-described disposition of the arm 4, the distance towhich the cutter protrudes with respect to the end 18, is as small aspossible, and, with the lever 8 disposed on the end 19, the cutting zoneis clear and allows the cutting of gears mounted on short rigid arbors.

The above makes it possible to increase the rigidity of the cradleconstruction in the course of the cutting process and, therefore, raisesthe precision of cutting of gears.

The tool holder 5 disposed on the arm 4 is of a standard design andallows control of the angle of inclination of the cutting edges of thecutter by means of a wedge 20 of conventional construction of the typeas shown in U.S. Pat. No. 2,101,237, and, in this way, to vary theeffective pressure angle of the gear being machined, and to obtain arequired disposition of the tooth bearing pattern with regard to thetooth height.

To mount the cutters and to obtain the required disposition of the toothbearing pattern with regard to the tooth length in the course of meshingof gears being manufactured, the tool holder 5 is made so that it can bedisplaced vertically along guiding faces 21 of the arm 4 by a screw 22(FIG. 2) and be fixed in a required position by screws 23.

The crank gear assembly essentially comprises crank plate 24 (FIG. 2)having an adjustable crank pin 31 mounted thereon, plate 24 beingsecured on the drive shaft 13. The pin 31 is hinged to a connecting rod25. To adjust the length of the connecting rod 25 when adjusting theslides to the length of the distanceof a gear being cut, the connectingrod 25 is made of two portions 26 and 27, which are interconnected by ascrew 28 and a nut 29, portion 26 of the connecting rod 25 beingconnected by means ofa spherical bearing 30 to crank pin 31, and theportion 27 being secured by means of a spherical joint 32 to the slidearm 4.

The shaft 13 of the crank gear is rotated through a pair of gears 33 and34, the axis of rotation of the driving gear 33 coinciding with the axisof rotation of the cradle generating drum 1.

To adjust arms 4 to the cone distance of the gear to be cut, carriages35 (FIG. 1) are provided on which the axles 9 of the levers 8 aresecured. The carriages 35 are disposed in guides 36 in the end 19 ofsegments 2, and the carriages are displaced by hand by turning a roller37 carrying a gear 38 which engages a tooth rack 39 mounted on thecarriages 35. The displacement of the carriages 35 results indisplacement of the lever 8 and arm 4 so that the axle 7 of the arm 4moves to a required position according to the cone distance of the geargeing cut and this is indicated by a knob 40.

The cradle drum 1 houses a hydraulic cylinder 41 (FIG. 2) whose rod 42is provided with the gripper 3 capable of engaging the flat end 15 ofthe pusher 10. The pushers 10 push against both levers 8 turning thelatter around their axles 9, and impart a longitudinal displacement tothe arms 4, as a result of whichboth cutters 6 are extracted from thetooth space of a gear being machined during the period of cradle returnrotation.

Due to withdrawal of the tools instead of the gear the movement of heavyparts of the machine is decreased, which, in turn, results in anincreased precision of the machining of the teeth.

In the ourse of machining the teeth of a gear by the gear-cuttingmachine the cradle operates as follows.

The gear 33 is driven and, through the intermediary of the gear 34 theshaft 13 of the crank 24 is driven. The crank 24 operates the connectingrod 25 which causes rocking of the arm 4 with respect to the axle 7. Thecutter 6 secured on the arm 4 rocks therewith along the tooth of a gearbeing out along an arc centered on axle 7. The length of this radiusbeing relatively great, the circumference of the bottom of the space ofa tooth being cut differs only insignificantly from a straight line.

From the shaft 13, on which the cam 12 is secured, movement is impartedthrough the roller 14 to the pusher 10, whose flat end 15 causes thelever 8 to rock on the axle 9. Since the axle 7 of the arm 4 is disposedon the lever 8 and the arm 4 and levers 8 are in a mutuallyperpendicular relation, the arm 4 is given a longitudinal displacement,and the cutter 6 performs an additional movement which is perpendicularto the main one and allows extraction of the cutter 6 from the toothspace of a gear being cut at the end of the forward stroke andintroduction into the space upon completion of the reverse or returnstroke, it being understood that the movement of arms 4 are so timedthat when one tool performs its working stroke, the other tool performsits return stroke.

The combination of the main and additional movements of the arm 4 makesit possible to obtain a trajectory of movement of the cutter 6 forcutting a tooth. The time and distance, for which the cutter has to beretracted, are determined by the shape of the cam 12 only. By usingvarious cams it is possible not only to 5 preset any required trajectoryof the cutter movement,

To set the arms 4 in accordance with the length of thecone distance of agear being cut, it is necessary to turn the roller 37 by the gear 38 andto displace through the intermediary of the toothed rack 39 the carriage35 along the guides 36, as well as to respectively change the length ofthe connecting rod 25.

With the cradle operating stroke completed, in order to extract thecutters from the tooth space of a gear being cut, pressurized oil issupplied to the cylinder 41, which result in displacement of the gripper3 with the rod 42, and, hence, of the pushers of both slides interactingwith the gripper '3. While moving, the pushers 10 turn the levers 8 in aclock-wise direction around the axle 9, which results in a longitudinaldisplacement of the arms 4, corresponding to the extraction of bothcutters 6 from the tooth space of the gear being cut.

The extraction of the cutters from the tooth space of a gear being cutduring cradle reverse rotation makes it possible to dispense withdisplacement of such bulky parts as the table with the workpiece stocksecured thereon, which, in its turn, allows increase of the precision ofthe cutting of gears.

The proposed design of the cradle with insignificant constructivealterations may be employed in machines used for machining the teeth ofspur gears, especially in instances where a generating workpiece isdriven by a belt drive.

Though in describing the present embodiment of the invention, specificnarrow terminology has been used for the sake of clarity, the invention,however, is not limited to the terms used, as each such term embracesall equivalent elements operating analogously and used for achieving thesame tasks.

Though the present invention is described in connection with thepreferred embodiment thereof, it is evi dent that alterations andmodifications can be made without departing from the spirit and scope ofthe invention as those skilled in the art will readily understand.

Such alterations and modifications are considered to fall within thesubject-matter and scope of the invention and the appended claims.

We claim:

1. A cradle for a bevel gear generating machine, the cradle beingadapted for being driven in rotation and comprising two segments mountedtherein, a slidably mounted tool holding arm in each segment, a pivot oneach one of said arms, two levers each pivotably connected to one ofsaid arms at a respective of said pivots, first drive means for swingingeach arm relative to its associated lever about its respective pivot,means sup porting each lever for pivotable movement about a pivot axisspaced from the pivot by which the lever is connected to its associatdarm, and second drive means for rotating said levers about their pivotaxes in directions substantially perpendicular to the pivotable movementof the respective arms relative to said levers so that the combinedpivotal movements of each lever and its respective arm can move eachtool along a predetermined closed path.

2. A cradle as claimed in claim 1 comprising guides in said segments forslidable support of the tool holding arms, said guides being arranged sothat the respective arm moves in a plane which is inclined to the axisof rotation of the cradle at an angle substantially equal to thepressure angle of the generating tool.

3. A cradle as claimed in claim 1 comprising-adjusting means foradjusting the position of the pivot axis of each tool holding arm to thecone distance of the gear to be machined, said adjusting meanscomprising, for each tool holding arm, a carriage mounted in a guideprovided in a respective segment, an axle on said carriage supportingsaid lever for pivotable movement about said pivot axis, and means formoving each carriage.

4. A cradle as claimed in claim 1 comprising a hydraulic cylindercarrying gripper positioned to turn the levers about their pivot axesfor withdrawing the tools from the workpiece.

5. A cradle as claimed in claim 4 wherein said first drive meanscomprises a crank drive including a connecting rod connected with acorresponding tool holding arm to swing the latter to and fro and saidsecond means comprises a cam means coupled with said crank drive forcausing the respective lever to oscillate about its pivot axis to movethe respective tool along its predetermined closed path.

6. A cradle as claimed in claim 5 in which said connecting rod is ofadjustable length so as to adjust the position of the tool holding arm.

1. A cradle for a bevel gear generating machine, the cradle beingadapted for being driven in rotation and comprising two segments mountedtherein, a slidably mounted tool holding arm in each segment, a pivot oneach one of said arms, two levers each pivotably connected to one ofsaid arms at a respective of said pivots, first drive means for swingingeach arm relative to its associated lever about its respective pivot,means supporting each lever for pivotable movement about a pivot axisspaced from the pivot by which the lever is connected to its associatdarm, and second drive means for rotating said levers about their pivotaxes in directions substantially perpendicular to the pivotable movementof the respective arms relative to said levers so that the combinedpivotal movements of each lever and its respective arm can move eachtool along a predetermined closed path.
 2. A cradle as claimed in claim1 comprising guides in said segments for slidable support of the toolholding arms, said guides being arranged so that the respective armmoves in a plane which is inclined to the axis of rotation of the cradleat an angle substantially equal to the pressure angle of the generatingtool.
 3. A cradle as claimed in claim 1 comprising adjusting means foradjusting the position of the pivot axis of each tool holding arm to thecone distance of the gear to be machined, said adjusting meanscomprising, for each tool holding arm, a carriage mounted in a guideprovided in a respective segment, an axle on said carriage supportingsaid lever for pivotable movement about said pivot axis, and means formoving each carriage.
 4. A cradle as claimed in claim 1 comprising ahydraulic cylinder carrying gripper positioned to turn the levers abouttheir pivot axes for withdrawing the tools from the workpiece.
 5. Acradle as claimed in claim 4 wherein said first drive means comprises acrank drive including a connecting rod connected with a correspondingtool holding arm to swing the latter to and fro and said second meanscomprises a cam means coupled with said crank drive for causing therespective lever to oscillate about its pivot axis to move therespective tool along its predetermined closed path.
 6. A cradle asclaimed in claim 5 in which said connecting rod is of adjustable lengthso as to adjust the position of the tool holding arm.